The digital differential comparator, shown in FIG. 1, has been used in Dynamic Random-Access memories (DRAMs), as well as Static Random-Access memories (SRAMs). However, this circuit usually finds application in the data path external to the memory array itself, amplifying the data signal received from the memory array and passing it on to the output buffer. Since this circuit lacks any ability to write-back onto the input nodes, and since it is somewhat more complex than the traditional latching sense amplifier, shown in FIG. 2, it does not normally find use in the memory array itself.
Ferroelectric memories are superior to EEPROMs and Flash memories in terms of write-access time and overall power consumption. They are used in applications where a non-volatile memory is required with these features, e.g. digital cameras and contact less smart cards. Contact less smart cards require non-volatile memories with low power consumption as they use only electromagnetic coupling to power up the electronic chips on the card. Digital cameras require both low power consumption and fast frequent writes in order to store and restore an entire image into the memory in less than 0.1 seconds.
A typical read access of a ferroelectric memory consists of a write access followed by sensing. To illustrate, a xe2x80x9c0xe2x80x9d is written to the ferroelectric capacitor to discover the original data content of the memory cell. If the original content of the memory cell is a xe2x80x9c1xe2x80x9d, writing a xe2x80x9c0xe2x80x9d reverses the direction of the polarization within the ferroelectric capacitor. This induces a large current spike on the sense wire. On the other hand, there is no current spike on the sensing wire if the original content of the ferroelectric capacitor was also a xe2x80x9c0xe2x80x9d. Therefore, by sensing the presence of a current spike on the sensing wire, the original data of the accessed ferroelectric capacitor are determined.
The read operation as described is destructive since a xe2x80x9c0xe2x80x9d is written to any memory cell that is accessed for a read. The original data, however, are saved in the sense amplifier and can be restored back into the accessed memory cell. In other words, a read access is only complete after the second write that restores the original data.
A sensing circuit with independent write-back capability includes a sense amplifier that receives an input and a reference signal and a tri-statable write-back block receiving a write enable signal and the sense amplifier""s output signal. An optional data buffer also receives the sense amplifier""s output signal.